1. Field of the Invention
The present invention relates to the technical field of wavelength monitoring and, more particularly, to a high-resolution wavelength monitoring device of tunable laser source and method thereof.
2. Description of Related Art
The rapid development of network technology leads to an increasing use of optical fiber communication. The optical fiber communication provides a low-loss and very high information transmission capacity. With the dense wavelength division multiplexing (DWDM) technique, an optical fiber is capable of simultaneously transmitting 16, 32, or more different wavelengths. In such a dense channel spacing, wavelength drift may cause a severe cross-talk problem. Thus, a wavelength monitoring on laser sources is very important. Moreover, tunable laser sources are very important components in DWDM systems, as for example, a spare light source having multi-wavelength switching output or a fast wavelength-switching device. As such, the fast wavelength tuning and multi-wavelength output factors must be considered in dealing with the wavelength monitoring for tunable laser sources.
Fabry-Perot (FP) etalon is commercially available for monitoring single-wavelength lasers, like distributed feedback (DFB) lasers. The Fabry-Perot etalon has a periodical spectral characteristic, and thus, it is good for monitoring a laser source with a single wavelength. It is difficult to apply a FP etalon to monitor a tunable laser and to detect the potential mode-hopping phenomenon of a laser source. Furthermore, although the Fabry-Perot tunable filter or arrayed waveguide grating (AWG) is applicable to monitor the tunable laser sources, its tuning speed or cost is not satisfactory. In addition, although the detection of transparent current or junction voltage of a single Fabry-Perot laser diode has demonstrated to reach a resolution of 0.01 nm wavelength, the requirement on the stability of temperature control is very difficult to achieve.
U.S. Pat. No. 5,825,792 discloses a “wavelength monitoring and control assembly for WDM optical transmission systems”, which is used in wavelength monitoring for single-wavelength DFB laser source.
U.S. Pat. No. 5,617,234 discloses a “multiwavelength simultaneous monitoring circuit employing arrayed-waveguide grating”, which can achieve a high accuracy discrimination of individual wavelengths of a WDM signal, and which is suitable for implementing in the form of optical integrated circuits. However, the major component employed is an AWG and there are a plurality of photodetectors required, which results in an extremely high cost in implementing the monitoring circuit. Therefore, there is a desire to improve the above conventional wavelength monitoring devices of laser sources to mitigate and/or obviate the aforementioned problems.